1. Field of the Invention
The present invention relates to cleaning methods and apparatus for removing particles from surfaces in electrostatographic reproduction machines such as copiers and printers. More particularly, it relates to a method and apparatus for removing charged and uncharged particles from the image-bearing surface of an intermediate transfer member in such a machine.
2. Description Relative to the Prior Art
Electrostatographic process apparatus or machines, such as copiers and printers, which produce or reproduce toned images on receiver sheets are well known. In such machines, a toner particle image is formed on a moving image-bearing member, and is subsequently transferred onto a suitable receiver sheet, such as a sheet of paper. The transferred toner image is then fused onto the sheet to form a hard copy. Such hard copy production can be repeated over and over when a plurality of copies is desired. In order to ensure the quality of each subsequently produced image, each such apparatus or machine usually includes a cleaning device for removing residual particles, for example, from the surface of the image-bearing member.
As disclosed, for example, in U.S. Pat. No. 4,081,212, issued Mar. 28, 1978 to Wetzer, and in U.S. Pat. No. 4,183,655, issued Jan. 15, 1980 to Umahashi et al., in one group of such apparatus, the toner particle image formed on the image-bearing member is ordinarily transferred directly from such surface to a receiver sheet which is fed through an image transfer nip that is formed by the image-bearing member and a back up transfer-nip roller. During such transfer, the transfer-nip back up roller directly contacts the back of the receiver sheet in areas where such sheet is present, but undesirably also contacts the image transfer member in areas where there is no sheet. As such, the transfer-nip back up roller can become contaminated with toner and other particles which transfer from the image-bearing member onto the roller in such no-sheet areas. Accordingly, means are usually provided for cleaning such back up rollers as disclosed, for example, in the above-cited patents.
Another group of such electrostatographic machines or apparatus are disclosed for example in (a) U.S Pat. No. 4,712,906, issued Dec. 15, 1987 to Bothner et al., (b) U.S. Pat. No. 4,588,279, issued May 13, 1986 to Fukuchi et al., and (c) U.S. Pat. No. 4,899,198, issued Feb. 6, 1990 to Mahoney. This group includes those machines or apparatus capable of producing color images. As disclosed, each of them includes either a transfer member (TM) or an intermediate transfer member (ITM). In those machines that include a transfer member (TM), the toner particle images are formed on the image-bearing member, a receiver sheet is attached to the transfer member (TM,) and then moved repeatedly, for example, through an image-transfer nip formed by the TM and the image-bearing member for receiving the toner images thereonto. In those machines that include an intermediate transfer member (ITM), the toner particle images formed on the image-bearing member are first transferred to the ITM before they are then transferred from such ITM to a receiver sheet. The ITM therefore forms a pair of toner image transfer-nips, one with the image-bearing member and the other with a back up transfer-nip roller. The transfer-nip roller forms a transfer nip with the ITM through which the sheet is fed for receiving the toner images from the ITM. As discussed above, the back up transfer-nip roller in this case can similarly become contaminated with toner particles and must therefore be cleaned.
Additionally, however, the TM and the ITM can and do also become contaminated with residual toner particles as well as with other particles, for example, paper dust particles from sheets such as sheets of paper carried by the TM or fed into contact with the ITM. Such contamination of the TM or ITM is particularly a problem when different color toner particles are used to form a multiple color toner images in such machines.
Because the residual particles which contaminate transfer assist members (TAM) such as the transfer nip back up roller, the transfer member TM or the ITM include toner as well as other particles such as dust particles, some of such particles, as can be expected, will be charged and others will be uncharged. Furthermore, in the case of charged particles, the exact polarity of each particle is ordinarily not known precisely. Therefore, attempting to remove all such particles from a TAM (transfer assist member) merely by reversing the relative polarity of such a member can often be significantly ineffective. The alternative, of course, is to use a separate and dedicated cleaning device.
Such cleaning devices for removing contaminating particles from an ITM are disclosed, for example, in the above cited patents U.S. Pat. No. 4,588,279 and U.S. Pat. No. 4,899,198. Such cleaning devices, however, are usually separate or bulky and expensive. In addition, the effectiveness of each may still be detrimentally affected by the presence of charged and uncharged particles among such particles on the ITM.